The present invention relates to a method of manufacturing a metal part coated with a layer of polycrystalline diamond as well as a metal part obtained by such a manufacturing process.
The invention relates in particular to a method for manufacturing a part made of titanium or titanium alloy covered with a polycrystalline diamond layer as well as a titanium part obtained by this manufacturing process.
Titanium and titanium alloy parts designate metal parts whose principal component is titanium, which may or may not be alloyed with other elements in a lower concentration.
An alloy very commonly used for manufacturing such parts is the alloy known as "TA6V" alloy.
It is known that titanium alloys, particularly the TA6V alloy, have good mechanical characteristics, particularly good tensile strength, good resistance to fatigue, corrosion, and creep, and a relatively low density. These alloys are hence widely used in the aeronautical and space industries.
It is also known that titanium has very good biological immunity and is hence widely used in the biomedical field.
However, titanium alloys have poor wear resistance, particularly when they are in contact with a metal or a metal alloy and a high friction coefficient with a large number of materials.
In addition, titanium alloys can have a certain toxicity due to the presence of other alloy elements.
To remedy these drawbacks, a carbon layer for example is deposited on the titanium alloys, for example in the form of a polycrystalline diamond layer, which, depending on the utilization of the alloy, allows wear resistance to be increased and biological immunity to be improved.
At the present time, the polycrystalline diamond layer is deposited on the metal part at a high temperature, in the range from 800 to 850.degree. C. which, upon return to room temperature, triggers the appearance of very substantial residual stresses, on the order of 7 GPa, in the diamond layer. Present-day techniques of coating a part with a diamond layer hence do not allow diamond layers of greater thickness than 1 micron to be deposited without their flaking off upon cooling.
Moreover, diamond deposition at high temperatures brings about relatively high diffusion of carbon into the underlying metal, which causes deep changes in the intrinsic mechanical properties of the underlying metal.
The attempt has been made to remedy these drawbacks by depositing a polycrystalline diamond layer on a metal substrate at a lower temperature, for example less than approximately 700.degree. C. Deposition at such a temperature allows a thicker layer to be obtained, but adhesion of the diamond to the metal is relatively poor.